ATLANTA -- Pitching in a city where he always has success and is near his offseason home would appear to be the perfect situation for Jon Lester to get back on track.

The Atlanta Braves, though, have a new ballpark, and things definitely aren't normal for the Chicago Cubs left-hander.

Lester, who faces the Braves at SunTrust Park on Monday night, is coming off the worst outing of his successful 12-year career.

The winner of 151 major league games went into the All-Star break after giving up 10 runs (four earned) while getting just two outs against the Pittsburgh Pirates on July 9.

Lester had never failed to pitch at least four innings in his previous 334 starts.

"Nothing I can say can justify or give you a reason," Lester said afterward. "It's embarrassing."

The loss dropped Lester -- a 19-game winner a year ago -- to 5-6 and raised his ERA to 4.25. He had a 2.44 ERA last season. Lester allowed a grand slam among two homers and walked three against the Pirates.

Lester's struggles mirror those of the defending World Series champion Cubs (46-45), who got back over .500 with an interleague series sweep at Baltimore over the weekend, climaxed by trade acquisition Jose Quintana's scoreless outing in his first start Sunday.

The improved Braves (45-45) are also coming off a sweep, winning three games at home against the Arizona Diamondbacks.

Lester is 4-1 with a 1.95 ERA in five career starts in Atlanta, but all of those were at Turner Field.

Julio Teheran, who will start for the Braves against Lester, knows there is a difference between the old pitcher-friendly ballpark and SunTrust Park.

Teheran, who thrived at Turner Field, is 1-6 with a 7.58 ERA in nine home starts this season compared to 6-0 with a 2.53 ERA in nine road outings.

"It shouldn't matter where you pitch, but you want to pitch good here," Teheran said. "This is where you play the most games. I want to be better."

Teheran, who is 7-6 with a 4.79 ERA overall, pitched well in two road outings before the All-Star break, allowing seven hits and two runs in 13 1/3 innings.

The right-hander from Colombia has pitched well in his career against the Cubs, going 2-0 with a 3.11 ERA in six starts.

Despite their 35-victory difference in records last season, the Braves split six games against the Cubs. One of Chicago's two victories in Atlanta came from Lester, who won 8-2 on June 12.

Lester is 2-0 with a 0.42 ERA against Atlanta in his last three starts, all Cubs victories.

The Braves had a 43-30 regular-season edge over the Cubs in 20 seasons at Turner Field.

Atlanta lost 93 games last year and 95 games the previous year, but a victory against the Cubs in the series opener would give them a winning record for the first time since June 1, 2015.

"Getting to .500 is a hurdle. It's nice to get there," Braves manager Brian Snitker said. "But the way we've played, I feel we should be about five over instead of at .500."

Atlanta slugger Matt Kemp added, "We've got the defending champions coming in. There should be some good baseball. We've got to keep going."